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Rafter Bearing

BN4537

BN4537

SAWHORSE
Joined
Sep 10, 2020
Messages
901
Location
Kansas
We have a residential builder in our jurisdiction who frames his roofs the old way with rafters, instead of using trusses like everyone else. So, when we inspect his projects, one of the main things we look at is the bearing of the rafters on the top plate.

So, we have written him up multiple times for having the rafters bear on the toe of the cut rather than the heel of the cut (see pictures). By cutting/notching the rafters this way, he reduces the depth of the rafters, allowing the rafter to split along the grain and greatly reducing the span of the rafters. This issue could be solved by using longer rafters and raising the roof a few inches to bear on the heel of the cut, or by changing the pitch of the roof slightly to bear on the heel of the cut, but the contractor does not like either option for complicated reasons.

The structural engineer he hired is telling him that cutting/notching in this way is a non-issue, which I can accept on a case-by-case basis, but I am not comfortable using that as a blanket rule of thumb.

Is there any way the pictures I am showing are a prescriptive method of rafter bearing or cutting/notching? How do other jurisdictions handle this?IMG_0664.JPGIMG_0665.JPGIMG_0600.JPG
 
Interesting that he uses glulams for the corner rafters. That would seem to be a touch of quality.
 
The first pic is engineered lumber, so only an engineer can approve the notch as the manufacturer won't....Non-prescriptive and fails at least two code sections..
 
Beniah Naylor said:
The structural engineer he hired is telling him that cutting/notching in this way is a non-issue, which I can accept on a case-by-case basis, but I am not comfortable using that as a blanket rule of thumb.
Click to expand...
Does the SE recommend H3 twist ties or is three nails enough?
e hilton said:
Interesting that he uses glulams for the corner rafters. That would seem to be a touch of quality.
Click to expand...
E hilton, I'm seeing gluelams being used for hip rafters a lot more in the field, probably due to inventory issues. I would think they would be cost prohibited. I'm seeing that cut on the hip rafter at the top plate like the photo.

How's the ceiling finish out with the hip rafter down below the commons and hip rafters?
 
Pcinspector1 said:
Does the SE recommend H3 twist ties or is three nails enough?

How's the ceiling finish out with the hip rafter down below the commons and hip rafters?
Click to expand...
The SE does recommend the H3 hurricane ties as the only fix for all of the above.

I believe that they normally install some kind of 2x4 ceiling joist and put in a flat ceiling, so that the rafter cut is at the same level as the ceiling joists. I will pay more attention on finals, I hadn't thought about that...
 
This contractor uses PSL sometimes, regular SPF other times, but notches/cuts like this all of the time. He told me that it was cheaper to use shorter lumber cut this way and pay an engineer than to get longer lumber and bear prescriptively. But he's getting tired of paying an engineer to come look at every house he builds...

So, I was always told that bearing on the toe of the cut and not on the heel is non-compliant, but what code section says that rafters have to have full bearing? I'm kind of stuck for a code section that specifically addresses this problem, I have been using R801.2 (Roof construction need to be strong enough to support all the loads), and 806.2 just says that the ends of each rafter shall have 1 1/2" of bearing.

All of the pictures shown have 1 1/2" bearing, just not where it supports the full rafter.

If someone here knows a better section or sections to reference, I would appreciate it - I would like something a little more substantial to work with.
 
A roof I-joist is cut that way and they attach to the top plate and add web stiffeners.

I'm not finding anything that shows the connection without a birds mouth cut. Bearing should be a minimum of 1.5" as you noted.

You might send the AWC a question to see if they have a diagram or comment?

H3's for sure to help prevent uplift appear to be a solution. Not sure blocking between at the top plate would help?
 

See article on "Are Birdmouths in Rafters Necessary?" JLC, The Journel of light construction​

 
Try R502.8, look specifically at R502.8.1 for sawn lumber and R503.8.2 for engineered wood. They reference that all cuts, notches & bored holes for joist, rafters & beams shall follow these code sections
 
Ask him for a calculation showing that the shear capacity of the hip is adequate at the bearing point.

Bending moment is maximum at near midspan and minimum at the bearing, but shear is maximum at the bearing.

Since the roof sheathing is already on I don't see how he will install ceiling joists to act as ties. Therefore the hip is acting as a beam. I often specified LVLs for hips because the moment with a 20 PSF live load was too much for a 2x12 once the hip length reached 16 ft.
 
We don't know the span of the hip rafters, the tributary loads, nor the minimum nominal dimension required. So if the building oversized the hip rafters to allow for the cuts, say using 2x10 where a 2x6 is only required, then would you allow it?
 
I would feel better about it, but I would think it would be similar to a builder ripping a 2x10 down to 2x6. It would probably work, but wouldn't it void the stamp on the lumber? So then are you using unstamped lumber? Which would have to be engineered anyway?

I accept that in the field sometimes, when a 2x6 is required and they still had more than the nominal 2x6 dimension, but I don't know if it is technically permissible.
 
Last edited:
The stamp on the lumber is specific to the grade, it does not regulate the cutting of the lumber. If a No.2 DF 2x10 were reduced in dimension, the grade is still the same. As for removing the stamp, if the inspector is wanting to see the stamp, be sure to cut so as to leave it on the rafter. Or be sure to safe the pieces with the stamp to show the inspector. The Building Official is the one who has ultimate decision on the matter. (R104.11)
 
# ~ #

Beniah, ...can you hold or deny the permit until
compliant documentation is provided in the
plan review process ?

# ~ #
 
We don't require bearing details for rafters in plan review, so if rafters are shown on the prints it is assumed that they will be installed in accordance with R802.7.1. The inspector gets to the field, sees that it does not comply with R802.7.1, and writes it up. The engineer is hired, he comes in and looks at it, he provides us with a letter stating that the rafter can support all loads as required by the building code, we approve it and move on. Rinse and repeat. It is still going on to this day.

It should be noted that no engineer or architect is required to design IRC house plans in our jurisdiction, so the plans that are used and re-used were not originally drawn by an engineer.
 
# ~ #

Is your Bldg. Official satisfied with the engineer's reports
on each project ?

# ~ #
 
# ~ #

If "said builder" would alter his framing methods, he
would be saving money on the engineer's letters.

FWIW, ...the cuts of the angles look pretty good.
From your pics. only, it doesn't look like bad framing.

% = % = %
 
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